Socket programming

Socket Programming in Python
Nemi Chandra Rathore
Department of Computer Science
Central University of South Bihar, Patna
August 25, 2017

Outline
Introduction
Nemi Chandra Rathore (Department of Computer Science Central University of South Bihar, Patna)Socket Programming in Python August 25, 2017 2 / 19

Introduction to Sockets
A socket is one endpoint of a two-way communication link between
two programs running on the network.[1]
process sends/receives messages to/from its socket.

Figure: Process communication on network using sockets(TCP)

A socket is bound to a port number so that the TCP layer can
identify the application that data is destined to be sent to.
On the Server Side:
Normally, a server runs on a speciﬁc computer and has a socket that is
bound to a speciﬁc port number.
The server just waits, listening to the socket for a client to make a
connection request.

On the Client-Side:
The client knows the hostname of the machine on which the server is
running and the port number on which the server is listening.
To make a connection request, the client connect with the server on
the server’s machine and port.
The client also needs to identify itself to the server so it binds to a
local port number that it will use during this connection.

Python provides two levels of access to network services [2]:
1 Low Level Access
Offers access the basic socket support in the underlying operating
system.
2 High Level Access
Offers libraries that provide higher-level access to specific
application-level network protocols, such as FTP, HTTP, and so on.

Sockets may be implemented over a number of diﬀerent channel
types: Unix domain sockets, TCP, UDP, and so on.
The socket library provides speciﬁc classes for handling the common
transports as well as a generic interface for handling the rest.

Term Decscription
domain The family of protocols that is used as the trans-
port mechanism. Indicated by constants like
AF INET, AF INET6, PF UNIX, PF X25 and so
on.
type The type of communications between the two end-
points, SOCK STREAM, SOCK DGRAM
protocol Used to identify a variant of a protocol, typically
0.
hostname A string representing host machine.(IP Address)
port A string containing a port number, or the name of
a service.
Table: Socket vocabulary

Socket Programming in Python: Creating a server
Import socket API using ”import socket” statement.
Create a socket, you must use the socket.socket() function available
in socket module
s = socket.socket(socket family, socket type, protocol = 0)
Example:
s = socket.socket(socket.AF INET, socket.SOCK STREAM)

Now bind the socket using bind function with a port and IP.
s.bind(IP, PORT)
This makes the server listen to requests coming from other computers
on the network on PORT
Now put the socket into listening mode by adding line s.listen(51).
1
5 indicates that 5 connections are kept waiting if the server is busy.

Now create a forever loop until we interrupt it or an error occurs:
accept and process any request from client within the loop.
Use s.accept() to accept a connection from client.
s.accept returns a tuple conn, addr where conn is a connection object
to the client and addr is address of the client.

Socket Programming in Python: Creating a client
Import socket API using ”import socket” statement.
Create a socket, you must use the socket.socket() function available
in socket module.
Connect the set server running at machine with (IP, port) pair using
s.connect((IP, port))
Now client can communicate using send() and recv() methods of the
socket object.

Table: Server Socket Methods
Method Decscription
s.bind() This method binds address (hostname, port num-
ber pair) to socket.
s.listen() This method sets up and start TCP listener.
s.accept() This passively accept TCP client connection, wait-
ing until connection arrives (blocking).

Table: Cleint Socket Methods
Method Decscription
s.connect() This method actively initiates TCP server connec-
tion.

Table: General Socket Methods
Method Decscription
s.recv() Receives TCP message.
s.send() Transmits TCP message.
s.recvfrom() Receives UDP message.
s.sendto() Transmits UDP message.
s.close() Closes socket.
socket.gethostname() Returns the hostname.

Protocol Common func-
tion
Port
No
Python module
HTTP Web pages 80 httplib, urllib, xml-
rpclib
NNTP2 Usenet news 119 nntplib
FTP File transfers 20 ftplib, urllib
SMTP Sending email 25 smtplib
Telnet Command lines 23 telnetlib
IMAP4 Fetching email 143 imaplib
POP3 Fetching email 110 poplib
Table: Python Internet modules
2
Network News Transfer Protocol

References I
Oracle: Java Documentation. https://docs.oracle.com/
javase/tutorial/networking/sockets/definition.html.
Accessed: 2017-08-20.
Python Network Programming. https:
//www.tutorialspoint.com/python/python_networking.htm.
Accessed: 2017-08-20.

Socket programming

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